Method of recovering uranium mineral values



July 15, 195s H. w.l LONG, JR

METHOD OF RECOVERING URANIUM MINERAL VALUES Filed' Jan.- 18, 1955 UnitedStates overblirdenv` coveringY Florida` pebble phosphate '-matriX,V

mainly'fou'nd in Polk County, Florida. Thek kleaclied zone material isfund in.I a stratified layer above the 'nifneable phosphate matrixan'dbelow the pleistocene sand overburden. yMc'gre particularly, theVinvention re` lates to the recovery of phosphorugaluminum anduraniumvalues fromthis leached zone material. p u

` Mjnerlgical' 'studies indicate' tliatth Vs o-call'd le'ached ione,material i lcherfTally identified as a miXtu of hydratedy aluminumphosphate; calcium'aluminum phos-V phateand fine'v quartz claywith someunleached and p dually ies-cheri catciufri phosphate pebble.' the'latter bei stratified ybe'tvveen"l the true' leach'e'd zone`I andb theph'si` indicate that theeare major mineralfpha'ses voffquartz,Awavellit'e, and perhaps pseudo wavellite with someph'ases I' of'-feldsp'ar, fvluorapatite', kaolinite and'heavy minerals s'ch as Zirconand' rutile; The present invention'l'is-A directerrtofthe treatn'ieurofrhisqleached zone material Orio'revfraetiensin whiehth'e claylikeperrions ofthe lea'ched zione material predominate. Y

Y The' followingfv'analyses' ofv leached zone material was obtained byaveragingthe analyses obtained' from about' 2G0" dril1 core samples'procured over'a'n'area` of about 36` squarer'niles' in' Polk County,Florida.

Since'the vast percentagejof the'acidin'solublekniatefial is quartz andsince' it'l'has'la corserpaticleisize'than'- the`vv other4 materialscontained" in the'le`ached'zo1ie-beingf mined, ithasbeen'fond:advantageous but not necessaryl t'ofthe invention tosplitthe ore. aftery suitable comminu--. n tion ifdesired, into one fractionof 'smallparticleseand Y another fraction of coars'er'fparticles. vIt'is Vnot nie'ant by this vdiscussion to infer that theentireleaclnfedzone material would', not be. ar'r'fenabl to' processin'gin .pacf A cordance with the present invention. Hovvever', tliersfzlids".lare usually'splitatfrom'about 150 meslriipztoy about' e mesh afterhaving 4been slurried' with Water.r Y,Other V'mesh'splits may also beused commensurate with ein# cient operation ofthe comminutinandclassifying-equi@ mem. The fraction containing 'the panieies'smauer than4 this range has beenfoud'to be the morvaluable frafcji tion, While thefraction containingthe' particles largerv than this range is thefractiony Whicliis'predominantly quartz and, therefore, a discardmaterial.,

y* The -proces`s1`of` thefpi'es'ent inve tion4 preteIr'bly;I Y concernedwith' the jsolubiliziing'andreco e'ryofmineral values contained' in the'fraction Whose;particlesY are glfoun'df particularly: in" al type' ofintermediate zone" arent O 2,843,450 Ulatented July 15, 19758 ice showsa" typical split in mineral valnesbetvveen the `--i200 mesh fraction andthe` 27007nesh fraction;

Mineral Value Plus 200 u Meshy Percent Percent; P205- Y Y 5.44I 14.681-' A1203 1. 68 25. 34. CaO 5.' 53 9.' 19. F6203-- 1. 60 l 34. 11 U3Qa0. 0053 050299 Acid Insolubles 83; 08 38. 56

Leached zone material may be processed eitheron a so-called as minedbasis or a wet basis. If'the leached zone material is to be handledzinwet form', the material is slurried to about solidswitli water in a pitat the miningv point, pumped to a plant, and sub'j jected toaseries ofclassification and' thickeningop'era# tions. YFrom the classication step.there is' segregated a; +200 mesh .fraction which .roughly Vwillconstitute between about 25% and about 35% of the ,original minedmaterial. This; TZOUmesh fraction .is subjected' to smaller than 'about'"150 mesh; tableVv thickening and' filtering operations to. reduethemoisture contenu, 'l.`he. solids are dried'.l atia temperature V.ofabout C. and are then ready for treatmentfin accordance withthisprocess; kIf theminingrmeth'ordis a sjo-calleddrygminin'g method;the minedjmaterial is conveyed to a Vplantloh belts and'passedthrough aidry-ing unitj'suchgas Ya rotary kiln Where the 'solids' .emergeatclassification operations such as an air classifcationoperation torecover the -200 mesh fraction correspondi ing to that recovered in thevWetclassicationsystemf In the Wet classificationfsystem', thescreenednout' -t-l`4', mesh Vsize y*material VVVis Y comminuted forliberation .of con" stituents and the comminuted material subjected'ltol'siing The 200 mesh fraction is' the preferable starting mate rial'forthe subsequentproces'sing of-ftheinstantinvention? p Preferablythevprocess lof the instant'.invention'.coin-vv prises heat treatingleached zone material,..digesting the. heat treated, materialwith anaqueous solution of ani-f monium bisulfate, removing insolublematerialfromfhthef digest solution, Vprecipitating alum' from the'dige'st solu`tio1 1, removing precipitated alum from themotherliquor.'

removingy uranium values from the. mother liquorgsand recovering thephosphate values'from the resulting liquor v MoreV in detail, theleachedZone` material" is solution. heat treated in the temperaturerangevofzbetween about 30020. andabout 1400., thegptemperature treatmentbeing determined primarily, by the4 degree of recovery: soughtasregardsthe minerals. uranium, aluminum and phosphorus relatively orindividually...V If th'ezhighest possible 'recovery of all threeminerals is Asought simul`` taneously, then the `heat treatment`ispreferably in-'thce range of between about 400"V C. and about 700 C.Vlf, ouk the otherhand, high recovery of phosphate .isfsoughtand-recovery of aluminum `and uraniumfis incidental;

then' heat treatment inthe range of'betwceirl about 850 C. andlabout1000 C. lispreferred.V f

Whe recovery of phosphate is to be sacrificed in Afavor of recovery of'uranium and aluminumfthef'heat treat;v ment inthe range of between'about 650". C.'to about800fv C. Yis preferred. lt will be seenfromzthi's discnssionfplus-` Y reference tothe figurejthatforvariousmineral combina-L r tionsthere will be a'preferred.temperature range ofhear treatment. This heat treatment may becarredlouti vin kilns;l and the like; *Heatv treatment "or"calcia'tinhas K a marked Veiect Von the degree of dissolution ofitheminerals in the aqueous ammonium bisulfate :solution andllalsoa/Smarkedefect uponpthel filtration rat'ewhich Y has-hereto ore been oneof the primedeterrentstocliemi l cal'treatrnent'of leached zonematerial.

Heat treatment to be effective must be for a minimum period of about 1hour. Calcination at temperature for a period of from about 1 to about 4hours is required to obtain dissolution of the Various components inaqueous bisulfate leach solution within an economic digestion time..Preferably the leached zone material is calcined for a period of about 1to about 2 hours.

Calcined leach zone material is cooled to a temperature below about 300C. before leaching with aqueous solution. This may be accomplished bysuch means as blowing cold air through the material to speed it coolingor simply by storing the calcined product until heat has been dissipatedand it is needed for pro Lessing.

Calcined material is digested with an aqueous solution of ammoniumbisulfate. The calcined material is either slurried into a bisulfatesolution of proper strength, or slurried with water after which ammoniumbisulfate or ammonium bisulfate solution is added to the solids slurry.The acid dilution to some extent is dependent upon the physicalcharacteristics of the resulting slurry, i. e., since it is preferred tostir or otherwise agitate the reaction mix, the slurry must besuliiicently dilute to permit uidity and the wetting of the solidparticles, while at the same time attaining a homogeneous mixture.

In general, the amount of ammonium bisulfate added is correlated to alarge extent to the other reaction conditions; namely, the temperaturesat which the digesting and solubilizing takes place, the time ofdigestion, and the final total amount of bisulfate present in theslurry.

Depending upon the analyses of the particular leached zone processed,between about and about 105% acidulation is desired. This corresponds tothe addition of between about pounds and about 137 pounds of arnmoniumbisulfate per 100 pounds of leached zone material processed. Betweenabout acidulation and about acidulation is preferred, since in eachinstance the percent recovery of the valuable minerals in the leachedzone material is at the optimum or approaching optimum conditions.

The percent acidulation referred to in this description is calculated onthe basis of the reaction of acid sulfate with all of the iron,aluminum, calcium, or other significant cation constituents present inthe leached zone material. In other words, acidulation would be theaddition of that amount of ammonium bisulfate required to completelyreact with these components. For practical operating considerations andfrom economic considerations the amount of acidulation generally variesfrom about 75% to about 90% or about 97.5 pounds to about 117 pounds ofammonium bisulfate per 100 pounds of leached zone material processed.

The time of digestion required normally will range between about 0.5hour and about 6 hours, preferably between about 1 hour and about 2hours. Such digestion times are for operating conditions of atmosphericpressure. If superatmospheric pressures are used the pressure employedwill vary as well as the other reaction conditions depending upon anyspecific set of values maintained for reaction conditions. In general,the higher the superatmospheric pressure employed and the higher thetemperature employed, the shorter the contact time required fordigestion and dissolution of mineral values. Pressure digestion alsotends to lower the quantity of bisulfate required to solubilize a givenunit of constituent. On the other hand, there is no intention to inferthat superatmospheric or autoclave pressures are necessary, and thisprocess works entirely satisfactorily at atmospheric conditions. Thetemperature of digestion at atmospheric pressure conditions generallyranges from about 70 C. to about 100 C. For a digestion time of about 30minutes a temperature in the range of 75 C. to 85 C. is generallypreferred.

The digested material after treatmentV with ammonium bisulfate solutionis iiltered to remove the insoluble solids. At this stage of theprocessing, the slurry to be filtered generally has a specific gravityin the range of about 1.15 to about 1.35, with about 1.2 to about 1.3preferred. At this specific gravity, filter rates vary directly with theheat treatment temperatures, i. e., the higher the calcinationtemperature, the higher the filtration rate, although it is not impliedthat this is a linear function. Leached zone calcined at a temperatureof about 950 C. will have a filtration rate of about 12 to about 15gallons of slurry per hour per square foot of filter area. This iscomparable to a lter rate of about 1 to about 3 gallons of slurry perhour per square foot of iilter area when the leached zone material isnot calcined.

Filtration is carried out at temperatures as high as practical from anoperational point of view. Generally, temperature of the slurry ismaintained at between about 50 C. and about 95 C.

Hot clear liquor recovered by filtration is cooled to precipitateammonium alum. Cooling to atmospheric temperature of about 20 C. toabout 30 C. will crystallize out most of the ammonium alum. If morecomplete removal is desired, the solution may be cooled to temperaturesin the range of about 0 C. to about 20 C. In general, substantiallycomplete alum removal is accomplished more cheaply by adding additionalammonium sulfate to the liquor rather than resorting to refrigeration.

To produce a substantially aluminum-free liquor, there generally isadded about one-third to about one half as much ammonium sulfate as wasoriginally present in the digestion liquor, i. e., about 30 pounds toabout 60 pounds of ammonium sulfate. Generally addition of ammoniumsulfate is made to attain an NH4/A12(SO4)3 mol ratio in the rangebetween about 1.011 and about 4.5 :1. Ammonium alum crystals are removedfrom the mother liquor by solid-liquid separation procedures.

Liquor substantially free of aluminum and suspended solids is subjectedto uranium recovery by use of solvent extraction as the preferredmodification. In solvent extraction the solution containing the uraniumdissolved therein is preferably rst subjected to a reduction reaction.This may be accomplished by electrolytic means or by chemical reactionwherein the solution is treated with metallic iron, aluminum, or certainfree metals or other reducing agents capable of reducing the solutionpotential but not substantially introducing metallic ions detrimental tospecications of final products. This reduction reaction is believed topartially, if not completely, reduce the uranium from a hexavalent stateto a quadrivalent state. If the addition agent is in powdered form, theslurry after several minutes is subjected to a liquid-solid separationto remove the unreacted and insoluble metal therefrom. This may beaccomplished through the use of a lter, centrifuge, cyclone or othersuitable separation device. Preferably, iron in the form of powder orfilings is used as the reducing agent. Aluminum may be used and in thisconnection aluminum could be added prior to alum crystallization so thatany dissolved aluminum could be recovered directly in the alum circuitand the reduced liquid then be subjected to solvent extractionprocedure. Solvent extraction of the uranium may be employed after alumremoval in an unreduced or only partially reduced state. The majordifference between the reduced and unreduced solution is that thereduced solution will require less theoretical extraction stages thanthe unreduced. In reducing the uranium bearing solution between about0.1 gram and about 8 grams of powdered iron, preferably about 2 grams,are added per liter of solution. The slurry is separated in a centrifugeand the reduced aqueous phase is then intimately contacted or otherwiseagitated with the organic solvent phase.

This extraction or solvent phase is made up of two components, theextractant and the vehicle or extender. The extractant may be one ormore of the ortho and/or pyrophosphoric acid esters of the alkylmonohydric alcohols. Both the monoand di-esters as well as mixtures ofthe two are useful. The butyl, amyl, hexyl, heptyl, N-

octyl, iso-octyl, decyl, etc., esters of phosphoric acid aresatisfactory for the purpose.v Phosphoric acidy esters of octyl andhigher molecular `weight alcohols are preferred since they are lesswater soluble. It is to be understood, of course, that other extractantswhich are relatively immiscible with the aqueous phase and havinguranium removal characteristics are likewise satisfactory. The extenderor vehicley may be any one or more of the common organic solvents suchas kerosene, benzene, naphtha,l mineral spirits, carbon tetrachloride,trichlorethylene, toluene, xylenes, and the like. Extenders such asthese are limited only in that they must be miscible or partiallymiscible with the extractant used and substantially immiscible with theaqueous phase. The concentration of th'e'extractant in the extender orvehicle -may vary widely, forexample, between about 0.2% and about 95preferably between about 5% and about 10%. The volume ratios-of' aqueousphase to organic phase may vary within wide limits, for example, betweenabout 1 to l and about 40 to l, preferably betweenA about 3 to l andabout to 1. It is preferred that the contact of the organic phase withaqueous phase be insuch apparatus as a mixer extraction column and thatthe contact be at a temperature of between about room temperature C.)and .about 60 C. A continuous extraction carried out in multistagecountercurrent extractors removes approximately 98% of the originalvalues originally present in results in the formation of ammoniumsulfatewhich can be removed by centrifuging. Following the recovery of ammoniumsulfate, the resulting liquor may be cooled to a temperature of about C.to about 30 C. to

crystallize out an ammonium phosphate contaminatedV with ammoniumsulfate. The ammonium sulfate and the ammonium phosphateammonium sulfateproducts may be puried by subsequent crystallization or drying forsaleas produced.

the aqueous phase to the organic phase. In a single stage of extractionutilizing the octyl ester of phosphoric aci`d ,`V30

.the ester being present in 10% solution vin keroseney andy :theextraction being done at a 10 to 1`volume ratio of` .aqueous phase toorganic phase, 95% of the uranium values present are transferred to theorganic phase.

Y AThe, organic .phasefisl treated withV aqueous hydrofluoric :acid orany other mixture capable of precipitating and/ or removing the U3Q8vfrom the organic phase as a iiuoride about. 5; molar'excess over thatrequired to produce UF4. This precipitate together with its accompanyingaqueous phase is separated from the organic phase and the solid UF4precipitate recovered by ltering centrifuging, or the like.

The aqueous phase after extraction of the .uraniumwith organic solventis treated to recover the predominantly phosphorus, nitrogen, and sulfurvalues-which are in solution in any number of compounds suchas arn-lmonium sulfate, ammonium acid sulfates,rminorramounts.v

. of miscellaneous metal sulfates and P205 values such as phosphoricacid or combinedpwith the metal or cationic valu'e'seas mentioned above.This aqueous solutionmay be adjusted in'pH or neutralized withoxygen-containing basic alkaline earth metal compoundsY or with suchreactants as ammonium hydroxide or ammoniagas orV others `which formsubstantially waterfs'oluble sulfates to l giveaprecipitation'ofinsoluble values, i.v e., aluminum phosphate and ironphosphate. Stepwise precipitation of iron and aluminum phosphate wouldbe accomplished rbyl neutralizing the solution to a pHrof aboutSLS,'separat-1 ing thefsolid's produced therein, and thenfurtherneutralizingthe solution to a pH of about 7 ytofformv a second' precipitate. IfvtherpH'of `the-'solutionis adjusted'with i ammonium hydroxide,lbestseparating conditions are ob7 tained it the original solution isneutralized to a pHabove about 9; andY preferably to about10g5. Atthisstage. the

Y' slurry is uid and `tlters or centrifuges with greater ease.

Upon removarofthe aluminum ork iron precipitate formedunder.ythese.conditions, the liquor resulting,` depending vupon theP2O5'ari'd ammonia concentration, may be processed to recover ammoniumphosphate values.

Ammonium sulfate recovered as heretofore described may be recycleddirectly for thermal decompositioninto ammonia and ammonium acidsulfate, both of whichl products can be reutilized in the process. `Since ammonium sulfate -is required in the primary alum crystallization,a portion of the ammonium sulfate is recycled directly with or withoutprevious drying.`

The invention will be furtherillustrated .byl the following examples. Y

EXAMPLE r Dry leached z'one material was air sized to produce a 500pound fraction of material passing through a 200 mesh standard screen.

815 C. for approximately one hour. p Y

Calcined material was cooled to approximately 100 C.

This Calcined material wasr mixed with an aqueoussolution consisting of52,0 pounds of ammonium bisulfatel and 1212 pounds ofwatertcorresponding to 80% acidulatals recovered from the solution whendry weighed ap-Y proximately 102 pounds; To this cool solution was addedapproximately 200 pounds of ammonium sulfate in by weight solution form.This addition of am- Ymonium sulfate crystallized out an additional 30pounds of alum crystals Al2(SO4)3.I(-NH4)2SO4;24H2'O. VThese crystalswere removed from solution by Ifiltration.

The solids free solution totaling approximately 290 gallons wassubjected to contactiwith about pounds of metallic iron ilings andpunchings in a packed tower.

Contact time Vfor the solution .wasabout l0 minutes per y unitof volume.

The reduced liquor was then lcontacted with organic solvent in thevolume ratio of 4 volumes ofl liquor to one i phase which was thenprocessed to recover P205, nitrogen and other values. Y I ATheruranium-,containing organic solvent' was treated on a volume basisof..0.-9,gallon. of 50% aqueousy hydro-V uo'ric acid per one gallon oforganic solvent. This mix-V ture separated into an ,aqueous slurry phase'andfanon Y ganic solvent phase. The aqueous slurry wasremoved and theyUFgprecipitate recoveredl by iiltration. Approximately 0.17 pound of.dry UF4' cake of`aboutr60% .ura

nium content is recoveredfperA gallons of aqueous ,solution'extract Y j.t p The aqueousv phase Ifatterfsolvent extraction YVwas'adf` Y justedto'af'pH ofvab'out 7 withf29`.% ammoniumhydroxjf 1 ide andfe'vaporatedto drynessto recoverja product ico/nl n tainingammonia, sulfateandphosphate, suitable for agri- Y Y culturalconsumption. 1 Y

, The. *200 mershfrarcton, ,was calcined in a rotary kiln at atemperature of aboutY Analytical results on various products of thisprocess were as follows: i

Pounds of constituent indicated aqueous ammonium bisulfate solution inan amount to provide between about 55% and about 105% acidulation,

A1303 C30 P205 F9203 S04 Uaos NH3 -200 Leached Zone (Feed) 159. 44. 594. 5l 9.0 431. 6 0. 165 78. 0 Digestion Cake 86. 2 41.13 23. 9 3. 9138. 2 0.055 14. 5 Digestion Filtrate. 56. 5 1. 38 73. 2 2. 3 205. 5 0.145 50. 6 Alum Crystals 20. 5 1. 5 0.029 73. 5 6.7

From the above data it is apparent that with calcining at 815 C. with80% acidulation 48.3% of the aluminum is recovered and 88% of theuranium present in the leached zone is recoverable.

EXAMPLE II Leached zone material was treated in all respects the same asin Example I, except that the calcining was at a temperature of 500 C.instead of 815 C.

Pounds of constituent indicated A1203 Cao P205 rego@ so. l Uio NH3 -200Leached zone mean--- se. 4 s. s 32. 2 1. s4 164. 47 0. 054 29. 11Digestion Entrata... 16. 9s .04 27. 7 1. a 02. 5o 0. 034 15. 52 AlumCrystals.-." 10. 5 0. 52 0.026 39. 6 3.7 Alum Free Liquor. 16.02 21. 60.033

4. EXAMPLE IH The method of claim 2 wherein said leached zone Pounds ofconstituent indicated material is the -200 mesh fraction obtained bysize 5 separation of` leached zone ore.

5. The method of recovering mineral values from leached zone materialcontaining uranium and aluminum The gure is a plot of percent recoveryof various minerals in the digestion ltrate versus calciningtemperatures in degrees centigrade. terial was calcined at temperaturesfor 1 hour and the calcined material digested with ammonium bisulfate at80% acidulation for two hours at a temperature of about 80 C.

Having thus fully described and illustrated the character of theinvention, what is desired to be secured and claimed by Letters Patentis:

1. The method of recovering mineral values from leached zone materialcontaining uranium and aluminum phosphate, from Florida phosphate pebbleoverburden, which comprises heat treating the leached zone material at atemperature in the range between about 300 C. and about 1100 C.,digesting the heat treated material with aqueous ammonium bisulfatesolution in quantity to give between about and about 105 acidulation,separating insoluble material from the digest solution containing watersoluble reaction products, and recovering at least one of the aluminum,uranium and phosphate values.

2. The method of -recovering mineral values from leached zone materialcontaining uranium and aluminum phosphate, from Florida phosphate pebbleoverburden, which comprises heat treating the leached zone material atatemperature in the range between about 400 and about 700 C., digestingthe heat treated material with The leached zone ma- References Cited inthe le of this patent UNITED STATES PATENTS Langlet et al Ian. 23, 1912Sanders Feb. 27, 1934 Hixson et al. Jan. 7, 1941 I-Iitchon et al Aug. 6,1946 Pires Oct. 16, 1956 FOREIGN PATENTS Canada May 25, 1954 OTHERREFERENCES Warf: U. S. Atomic Energy Comm., declass. paper No. ABCD-2524(Aug. 7, 1947), 10 pages.

Engineering and Mining Journal, vol. 155, No. 10, page 122 (October1954).

1. THE METHOD OF RECOVERING MINERAL VALUES FROM LEACHED ZONE MATERIALCONTAINING URANIUM AND ALUMINUM PHOSPHATE, FROM FLORIDA PHOSPHATE PEBBLEOVERBURDEN, WHICH COMPRISES HEAT TREATING THE LEACHED ZONE MATERIAL AT ATEMPERATURE IN THE RANGE BETWEEN ABOUT 300*C. AND ABOUT 1100*C.,DIGESTING THE HEAT TREATED MATERIAL WITH AQUEOUS AMMONIUM BISULFATESOLUTION IN QUANTITY TO GIVE BETWEEN ABOUT 55% AND ABOUT 105%ACIDULATON, SEPARATING INSOLUBLE MATERIAL FROM THE DIGEST SOLUTIONCONTAINING WATER SOLUBLE REACTION PRODUCTS, AND RECOVERING AT LEAST ONEOF THE ALUMINUM, URANIUM AND PHOSPHATE VALUES.